Explosive compositions containing technical grade 2,4,6-trinitrotoluene (TNT) are often cast into artillery shells, rockets, bombs, etc. by heating the composition to melt the TNT and then pouring the melt into the shell where it is allowed to cool and solidify. Cast changes thus obtained usually exhibit undersirable properties, such as exudation of oily impurities on storage, voids, poor compressive strength, brittleness, lack of homogeneity due to oriented crystal structure of the TNT, etc., which adversely affect ballistic performance and impact sensitivity. Various methods have been proposed to overcome such undesirable properties, but they have been only partially successful. For example, British Pat. No. 1,249,038 discloses that a fine crystalline cast charge of TNT having random crystal structure can be obtained by incorporating a small amount of hexanitrostilbene into the molten composition. However, the hexanitrostilbene is not effective for overcoming other deficiencies, such as brittleness, exudation, etc. Various additions to the molten TNT composition have been proposed to produce solid casts possessing increased resistance to exudation and cracking, e.g. high polymers soluble in the explosive, specifically poly (methylmethacrylate), polymethacrylate, and poly (isopropenyl methyl ketone) (West German Pat. No. 1646278, West German Offen. No. 2100030). U.S. Pat. No. 3,706,609 discloses that cast TNT explosives, which are free from exudation and voids and can be remelted and recast while retaining good homogenity, can be obtained by adding a thermoplastic cellulosic resin like nitrocellulose to the melt. However, the resulting cast charges are relatively brittle and possess relatively poor mechanical strength and adhesion to the artillery shell. U.S. Pat. No. 3,447,980 discloses the production of cast TNT explosives, which are essentially free from exuding oils and voids, are less brittle and possess superior compressive strength and adhesion to the case, by incorporating into the molten explosive composition a polyurethane elastomer producing system consisting of a prepolymer from 2,4-tolylene diisocyanate and 1,4-polybutylene glycol plus a curing agent. However, the molten explosive compositions have limited pot life before gellation and irreversible chemical curing of the polyurethane elastomer takes place; and the solidified compositions when remelted separate into a liquid TNT phase and a solid insoluble elastomer phase and hence cannot be reprocessed to produce a composition of constant explosive characteristics. U.S. Pat. No. 4,012,245 discloses the production of cast TNT explosive compositions, which are essentially free from oily exudation on storage and voids and can be remelted and resolidified essentially without loss of homogeneity and explosive properties, by incorporating in the molten explosive composition a small amount of a polyurethane elastomer-producing system consisting of an organic polyisocyanate, a hydroxyl-terminated 1,4-butadiene polymer liquid resin and an abietyl alcohol.
The polyurethane elastomer producing systems employed according to the foregoing patents are relatively complex and require the reaction in the molten TNT composition of a compound containing free isocyanate groups with a compound containing free hydroxyl groups. However, the presence of moisture in these systems must be avoided, since the water can react rapidly with the isocyanate groups to form gaseous carbon dioxide, causing inter alia the formation of harmful voids in the solidified cast. Such moisture can be introduced into the explosive composition in various ways and its complete removal can be difficult if not impossible. For example, in the manufacture of Composition B, consisting of 60% RDX and 40% TNT (plus added wax desensitizer), the RDX crystals mixed with the TNT may contain adherent moisture due to incomplete drying of the crystals after washing with water. Further, while such polyurethane producing systems are effective for overcoming some of the deficiencies of cast TNT compositions, they must be employed in conjunction with other additives to reduce or eliminate other shortcomings. Thus, it appears that prior to the present invention no single, broad spectrum additive had been proposed for treating the many problems associated with cast TNT charges.